A touch panel is widely known as an apparatus for detecting a position (hereinafter, also referred to as a “touch position”), on a touch screen, indicated with an indicator, such as a user's finger and a pen, for output. As a type of detection of a touch position in a touch panel, a plurality of detection types are known. One example of a touch panel of an electrostatic capacitive type is a projected capacitive touch panel.
The projected capacitive touch panel can detect a touch position even when a surface (hereinafter, also referred to as a “front surface”), of a touch screen, facing a user is covered with a protection plate, such as a glass plate, having a thickness of approximately several millimeters. The projected capacitive touch panel has advantages of being robust as the protection plate can be disposed on the front surface, having a long life as there is no movable part, and the like.
The touch screen of the projected capacitive touch panel includes detection column wires for detecting coordinates, of touch positions, in a column direction, and detection row wires for detecting coordinates, of touch positions, in a row direction (see, for example, Patent Document 1). In the following description, the detection column wires and the detection row wires are also collectively referred to as “detection wires”.
Patent Document 1 discloses a touchpad system, which corresponds to the touch panel. The touchpad system disclosed in Patent Document 1 includes, as detection wires for detecting electrostatic capacitance (hereinafter, also simply referred to as “capacitance”), a first series of conductor elements formed on a thin dielectric film, and a second series of conductor elements formed above the first series of conductor elements with an insulating film therebetween. There is no electrical contact between the two series of conductor elements, and the first series of conductor elements and the second series of conductor elements overlap each other when viewed from a direction normal to a front surface to form intersection portions without electrical contact.
A detection circuit detects capacitance (hereinafter, also referred to as “touch capacitance”) formed between an indicator, such as a finger, and the conductor elements, as the detection wires, to specify coordinates of a touch position indicated with the indicator. Furthermore, through use of relative values of detected capacitance for one or more of the conductor elements, a touch position between conductor elements can be interpolated.
In the following description, a member obtained by arranging detection column wires and detection row wires over a transparent dielectric substrate is referred to as a “touch screen”, and an apparatus obtained by connecting a detection circuit to the touch screen is referred to as a “touch panel”. A region, on the touch screen, in which a touch position is detectable is referred to as an “operation region”.
In order to detect the touch position indicated with an indicator at any positions in the operation region on the touch screen, it is necessary to densely arrange the detection wires in the operation region. In densely arranging the detection wires in the operation region as described above, it is necessary to avoid a problem in that the detection wires are visible to a user.
When the detection wires are formed by a transparent conductive film made, for example, of indium tin oxide (ITO), the possibility that the detection wires are visible to a user is reduced. However, the transparent conductive film made, for example, of ITO has a relatively high electrical resistance (hereinafter, also simply referred to as “resistance”), and thus has a problem in that it is disadvantageous in terms of an increase in size of the touch screen. In addition, the transparent conductive film made, for example, of ITO has a light transmittance (hereinafter, also simply referred to as “transmittance”) that is not so high, and thus has a problem in that a relatively large amount of light is necessary when the touch screen is illuminated from a back surface thereof, i.e., from a surface opposite a surface facing a user, by a liquid crystal display (LCD) and the like for use, and it is disadvantageous in terms of reduction of power consumption.
A low-resistance metal material such as silver and aluminum can be used as a material for the detection wires. Use of wires made of the metal material (hereinafter, also referred to as “metal wires”) as the detection wires can reduce resistance of the detection wires, but has a problem in that the metal wires are likely to be visible as they are opaque. In order to reduce visibility of the metal wires and to increase transmittance of the touch screen, it is necessary to make the metal wires fine.
When the fine metal wires are used as the detection wires, and densely arranged in the operation region on the touch screen, a problem of a significant increase in parasitic capacitance (hereinafter, also referred to as “line capacitance”) between the detection column wires and the detection row wires occurs, causing a harmful effect, such as an increase in wiring delay.
The wiring delay can be mitigated to some extent by reducing wire resistance. Technology for reducing wire resistance to mitigate the wiring delay is disclosed in Patent Document 2, for example.
A touch screen disclosed in Patent Document 2 ensures lower resistance and lower line capacitance by forming detection column wires and detection row wires by linear fine metal wires connected in a zigzag pattern.
In addition, in the touch screen disclosed in Patent Document 2, a plurality of detection row wires approximately extending in a row direction are electrically connected to one another to form a row-direction wire bundle, and a plurality of detection column wires approximately extending in a column direction are electrically connected to one another to form a column-direction wire bundle. This enables uniform detection of touch capacitance including capacitance between an indicator, such as a finger, and the detection row wires, and capacitance between the indicator and the detection column wires.
In the touch screen disclosed in Patent Document 2, however, transmittance locally decreases at portions where fine metal wires are arranged. When the touch screen is used in combination with a display device disposed so as to face a back surface of the touch screen, uneven luminance and uneven display, such as moire, of a display screen occur on a display screen of the display device, and are likely to be viewed as a malfunction by a user. When an illustration is disposed so as to face the back surface of the touch screen to use the touch screen as a digitizer or a tablet, uneven luminance of the illustration occurs, and is likely to be viewed as a malfunction by a user.
Technology for reducing uneven luminance and uneven display (hereinafter, collectively referred to as “uneven display”) is disclosed in Patent Document 3, for example. A touch panel disclosed in Patent Document 3 reduces uneven display by providing, in regions enclosed by detection wires in a zigzag pattern, isolated wires not connected to the detection wires.